60 The Cranial Nerves 



enters the upper surface of the superior oblique. Fibres of the nerve 

 decussate in the grey matter around the Sylvian aqueduct, so that 

 there may be harmony in the action of the two superior oblique 

 muscles when the head is turned. When the nerve is paralysed and 

 the head is moved sideways, the eye of the paralysed side moves with 

 the head instead of being steadily fixed upon the object, and the 

 subject sees double diplopia (8nr\ovs, double ; GIX//-, ton-os, eye). 



No. 5. The trifacial derives its name from its supplying the skin 

 of the face in three situations, namely, in the supra-orbital, infra- 

 orbital, and mental regions. It arises from the pons by two roots, 

 of which the anterior, or motor, is quite small ; the deep origin being 

 in the floor of the fourth ventricle. 



The sensory part of the nerve expands on the apex of the petrous 

 bone into the Gasserian ganglion, from the front of which come the 

 ophthalmic and the superior and inferior maxillary nerves. The 

 motor root takes an independent course beneath the ganglion, and 

 eventually leaves by the foramen ovale to join the inferior maxillary 

 trunk, the first and second divisions of the nerve being purely 

 sensory. 



Tic douloureux, or neuralgia of the fifth nerve or of one of its divi- 

 sions, maybe caused by pressure upon the main trunk, or upon its root- 

 lets in the floor of the fourth ventricle, or by pressure upon a trunk as it 

 leaves the skull or elsewhere in its course. Sometimes the distress is 

 due to peripheral irritation of a single filament, as in a carious tooth, 

 and amongst more remote causes are cold, dyspepsia, and nervous ex- 

 haustion. The pain may shoot along the filaments of the supra-orbital 

 or supra-trochlear nerve, along a division of the temporo-malar, or the 

 branches of the superior maxillary nerve in the cheek, nose, or upper 

 lip ; or along the twigs to the teeth, the temple, chin, lower lip, or side 

 of tongue. On any branch of the nerve there may be a specially 

 painful spot which the patient can precisely indicate. Sometimes the 

 attack is associated with flushing or sweating of the surface, and 

 sometimes it clears up with a profuse secretion of tears, nasal mucus, 

 or saliva, showing, as Ranney remarks, the implication of the vaso- 

 motor filaments in the nerve. This association explains also the inflam- 

 matory changes which the skin of the affected region may undergo, and 

 also the falling out or blanching of the hair which are sometimes 

 associated with the neuralgia. When the 4 tic 'is spreading, and is 

 associated with deep-seated headache and with paralysis of certain of 

 the motor nerves, a cerebral lesion may be suspected. Because there 

 is pain in the teeth it by no means follows that the teeth cause the pain, 

 and their extraction should not be hurriedly resorted to. 



Clavus is that variety of neuralgia in which the pain, though limited 

 to a single spot, is so * intense ' that the patient (generally an hysterical 

 young woman) feels as if a nail (clavus] were being hammered into 

 her flesh and bone. 



